I have a cordless landline phone module with a battery that needs to be replaced. The replacement battery is cheap (around 2 for $10), but just as a "fun project" I was going to see if I could create my own battery pack using two AAA NIMH batteries that I have on hand. The two that I would use have twice the amp-hour capacity as the replacement that I would order.
When it comes to recharging NIMH batteries, it is my understanding that one technique commonly used is to measure the temperature of the batteries to detect when they are fully charged. I think this is probably the method used by this cordless phone, as I noticed what appears to be 10 metallic "dots" underneath the battery pack (please refer to the attached photo). Can anyone confirm for me that these dots are indeed attached to some kind of temperature sensor inside this cordless phone used to measure the temp of the battery pack? If so, I would be sure to keep this in mind when building the replacement. Thanks in advance.

 

Show us the battery pack! I have never seen a cordless phone that sensed battery temperature. They all tend to use a current limited constant open circuit voltage to charge rather gently. Measure the open circuit voltage at the connection.
Those solder points are for phone programming or diagnostics. Look at the batteryu pack and observe that it has nothing to touch those points,.

 

The sensing of temperature is to keep your battery from turning into an explosive device. I suggest using a Li-Ion battery charging chip for this as it is a fairly complicated project without the chip.

Whatever approach you take, be very careful, and read up on Li-Ion charging. It might save your life or your home (or both!).

 

The sensing of temperature is to keep your battery from turning into an explosive device. I suggest using a Li-Ion battery charging chip for this as it is a fairly complicated project without the chip.

Whatever approach you take, be very careful, and read up on Li-Ion charging. It might save your life or your home (or both!).

Showing us a picture of the present battery pack will reveal that it connects only using the red and black wires going to that small connector.

 

see if I could create my own battery pack using two AAA NIMH batteries that I have on hand.

I suggest using a Li-Ion battery charging chip for this as it is a fairly complicated project without the chip.

The thread poster is talking about using NiMH batteries, which are probably what the cordless phone is designed to use.

A Li-Ion charging chip is completely wrong for this application.

 

The dots will not be indicating the temperature of the battery.

 

The dots will not be indicating the temperature of the battery.

Like I mentioned before: The battery connection is that tiny connector with the red and black wires. No temperature measuring and certainly no high power charging. Look at the battery pack and see what I mean.